In my family room is the KDL46EX500 (which is the model just below the one you mentioned) If I recall right, the main difference is that the 640 is a 120Hz TV where mine is the 60Hz variant.

I love the picture on it, I have been a fan of sony TVs. I don't feel you can go wrong with them. On the other hand, I have had a samsung TV die, although that is probably a one in a million chance of it happening.